The invention is directed to an apparatus and method for color blending differently colored batches of agglomerating flowable material together to fill a mold with a mottled heterogeneous charge including visible colored clumps of material from each colored batch.
A mottled, dappled or variegated random pattern is considered aesthetically pleasing in a number of applications providing a natural blended coloring. The irregular arrangement of blotches or patches of color in a multi-colored heterogeneous surface can be produced from flowable material which has been tumbled together or agglomerates naturally in a molding process.
In the specific example provided in the present description, a blended or mottled pattern is a desirable feature in the production of concrete paving stones and retaining wall blocks. In this art, using iron oxide pigments in the mix design of the concrete batch, the majority of paving stones and approximately one-half of retaining wall products are color blended.
In this art, the xe2x80x9cblendingxe2x80x9d of colors as used in this description and in the trade does not relate to complete mixing that would produce a homogenous color composite of the two input colors. Rather the word xe2x80x9cblendingxe2x80x9d relates to the mixing of two, three or sometimes four colored batches of concrete together such that the finished products contain distinct clumps or patches of each color consistently through the production of paving stones or retaining wall blocks.
An essential characteristic of such color blending is the consistency of distribution of each color used in the blending process throughout the production run. In the past, it has been extremely difficult to ensure consistency while retaining a random appearance to the finished product. Random mottling, with a consistent percentage of the surface area visible in each of the colors is the ideal. However, prior art systems are extremely dependent upon the skill of operators, result in wastage and unsatisfactory color blending in many cases. The capacity to produce a consistently blended product is advantageous in that wastage is reduced and the aesthetic appeal of the well blended product creates a significant market advantage.
Traditionally, because of the technical difficulties, most color blending has involved only two colors. The production of a consistently blended three color mottled pattern has involved extensive rework and generally unsatisfactory appearance in that the distribution of three colors is very sporadic and unpredictable. Mixing of four colors presents almost insurmountable difficulties for prior art systems. In many cases these difficulties can be addressed by manually mixing and laying the finished paving stones during installation with a trained eye to ensure even distribution of the different colors throughout the finished installation. A manual laying system increases labour costs and is generally inefficient in large areas where machined laying systems are preferred. In addition, the manual mixing of colored stones during installation relies heavily on the skill and perception of the installer.
In the past, color blending was carried out with a hopper having a separating bulkhead plate down the middle and filling the hopper with different colored materials on either side of the bulkhead dividing plate. A single gate at the bottom of the hopper was opened and blending of two colors occurred as both sides of the hopper were emptied simultaneously.
A refinement of this procedure included an upper hopper with a moveable plate gate serving as a funnel to feed a batch of colored material into either side of the lower divided hopper.
In the prior art, a concrete mixer was loaded with cement, pigment, sand and rock aggregate in the form of crushed stone chips or relatively small rocks, together with water and other admixtures to create a colored concrete batch. Once the raw materials are thoroughly mixed together, the mixer discharges the batch into the upper hopper and over the moveable plate to direct the flow of material into either side of the divided lower hopper. When the outlet for the lower hopper was opened, material from both sides of the hopper flowed out through the opening and tumbled together in a mottled blended charge into the mold.
There are several disadvantages to this prior art system. Firstly, when one side of the lower hopper is filled and other half of the lower hopper is empty, there is a significant amount of backflow from the filled side of the hopper to the unfilled side. As a result, the first portion of material which exits when the hopper is opened is a of single color. Generally, the first few fillings of the mold must be discarded since the aim is to produce a consistently colored mottled appearance using both colored batches.
In addition, since the extreme outward portions of the flow from the hopper are completely one color or the other, products produced in this manner generally have about 75% of the product blended in the central area of the mold, and the remaining outer 25% is evenly split between the two solid colors of the materials. Therefore, the degree of blending is satisfactory, but less than ideal, since a significant portion of the mold creates blocks that are a single solid color rather than dappled or mottled appearance as desired. These solid blocks can be distributed in the final installation, however with some skill on the part of the installer.
In prior art systems, the hopper does not drop material directly in to the mold, but rather the hopper deposits material into a filling tray. The material in the tray is agitated slightly to distribute material evenly and level the top surface, then the tray and material are transferred to a position above the mold. The filling tray has an open woven grate at the bottom and rests on a solid table during filling. An agitating grate distributes material and aids in the mixing of clumps of the different colored materials prior to depositing in the mold. When the filling tray is laterally shifted to above the mold, the relatively dry nature of the concrete mix and speed of lateral motion prevent the concrete from exuding through the bottom grating to any great extent. The mold and filling tray above it are then vibrated. Vibration agitates the thixotropic concrete mix in the filling tray to flow easily through the grating into the mold. The filling tray is removed, and a tamping head further vibrates and compacts the top surface of the material within the mold. Afterwards the mold and tamping head are withdrawn, and the finished blocks are conveyed away on a pallet.
This prior art system is generally accepted as the best that can be provided with existing equipment, however, the relatively large number of finished blocks of a single solid color with no blending of colors is a significant disadvantage. As well, the large amount of waste created when the first batch is dropped into one side of the hopper is disadvantageous, especially where a small production run or small number of batches is produced. With prior art systems, it is undesirable for a manufacturer to produce a short production run of blended product despite market demands since the wastage on starting up a production run becomes significant.
A further disadvantage of the split hopper prior art system is a slow cycle time and inefficient blending. Batches of colored material are gravity fed and ideally the amount of material stored in either side of the split hopper should be identical to result in the same quantity of flow when the clamshell gates are opened. However, since material is mixed in a single mixer, one color at a time, in general, the amount of material stored in one side of the split hopper will always be less than the amount of material stored in the other side. This results in uneven amounts of material flowing out when the hopper outlet is opened. For example, if one side of the hopper is full, the other side is almost empty awaiting refilling from the mixer, the volume of material flowing under gravity from the full side will be significantly greater.
It is generally undesirable to solve this problem by providing a larger sized hopper to store large quantities of wet materials, since the concrete mixture will set up and harden if not deposited in the mold within a limited period of time. It is not desirable therefore, for the dwell time of the wet concrete mix in the hopper to approach the setup time to avoid the difficulty of dealing with hardened material deposited within the equipment. In addition, the alternative of running mixers with less than a full batch load is inefficient economically and will slow down production.
The alternative of providing two more mixers is also not feasible economically. A mixer is an expensive capital item to purchase and operate. A mixer requires significant maintenance for proper operation and must be thoroughly cleaned after each production run. The additional cost of purchasing and operating separate mixer for each color generally cannot be passed on to the purchaser in the form of a significantly increased price for blended colored paving stones without detriment to the market for these products. A minor premium may be accepted, however, when significant production cost increases are experienced, in the form of additional equipment or slower production, these costs act to directly reduce the viability of the product line.
Problems with consistent mixing of various colors increase dramatically as the number of colors increase. For example, when three color blending is carried out in a two-part split lower hopper, the first batch is deposited in one side and the second batch deposited in the other side as explained above in respect of two color mixing. However, the third batch of a third color is then added to the same side of the hopper as the first batch. It takes a number of cycles before all three colors are seen exiting from the lower end of the hopper.
Significant wastage results on startup of production and it is extremely difficult to control the amount of each colored material which is being introduced into the filling tray. The skill of the mold press operator and experience accumulated over several trial and error attempts makes it never-the-less possible to produce a mottled three color blended product. However, the results are far from satisfactory and numerous complaints from purchasers are received since the colors are not evenly blended or sufficiently consistent.
Therefore, it is desirable to produce a system which allows for consistent color blending of two or more colored materials over a production cycle without the wastage or lack of consistency experienced with the prior art.
It is also desirable to provide a system where the blending of colors is predictable, consistent and reproducible through a single production run and between different production runs to ensure conformity of products to customer specifications.
It is highly desirable to provide a system where three, four or more different colors can be blended together consistently since this is practically impossible with prior art systems.
It is further desirable to produce a color blending system which can operate at the maximum speed of the molding press without prohibitively increased cost of equipment.
The invention provides a method and apparatus for color blending an agglomerating flowable material from a number of differently colored individual batches, such that a forming mold is filled with a mottled heterogeneous charge comprising material from at least two of the batches.
Differently colored batches of agglomerating flowable material are directed from a mixer to a like number of material storage hoppers each with an independently operable outlet. Once each hopper is initially filled, using sensing probes inside each hopper, the mixer continues to produce batches to maintain a sufficient amount of material in each hopper while the material flows out of the hoppers into the mold. Since each hopper has an independently operated outlet, differences in the volume of material in different hoppers can be compensated for and a predetermined volume of material can be dosed as required. Preferably the method includes a single mixer using a movable bucket operable between a loading position in communication with the mixer and a dumping position over a selected hopper.
Programmed controls directed by a computer for example then control the position relative to the mold, time sequencing and quantity of material passed through each hopper outlet to fill the mold with a mottled heterogeneous charge comprising material from at least two batches.
Preferably controls include indexing a filling tray to a number of selected tray filling positions relative to each hopper outlet. After being filled and levelled the filling tray is transferred to a mold filling position above the mold and the material is dropped into the mold.
A device for color blending includes at least two material storage hoppers each with an independently operable outlet, means to fill the hoppers directing a chosen colored batch of material from the mixer to a selected hopper, means to fill the mold, downstream from the hoppers, with material from at least two of the hoppers; and controls for controlling the position relative to the mold, time sequencing and quantity of material passed through each hopper outlet.
In the preferred example, the material is a relatively dry concrete mixture, known as zero slump concrete, which agglomerates into clumps that tumble randomly from the hopper outlets. By controlling the positioning of the filling tray relative to a selected hopper outlet, the time sequencing and quantity of material released from each hopper outlet, it is possible to fill the filling tray in a large number of seemingly random mottled patterns where clumps of each of the individual colors remain visible in the molded product. Although the mottled pattern appears random as is highly desirable, the distribution of color is controlled and can be rendered consistent within acceptable tolerances.
It is not desirable to produce identical mottled patterns in each charge delivered to the mold since the repeated identical pattern will be clearly apparent like a wallpaper pattern in the installation. The identical pattern would be particularly noticeable when blocks are installed by machine since the machine lays a complete layer course from a manufactured stack at one time. When laid by hand, there can be a degree of mixing that occurs if the installer randomly picks blocks from the stack, however this method relies on the knowledge and skill of the installer, and is prohibitively labour intensive on large projects.
A well blended stack of blocks should have a random appearance while including a consistent ratio of visible colored surfaces. The invention allows for a large number of variables in filling the mold so that a consistent random appearance is generated in a controlled manner. By programming the variance in the position, timing and volume of colored materials deposited from different hoppers, any number of different mottled patterns can be produced.
The natural characteristics of the material somewhat aid in producing a random mottled appearance since zero slump concrete for example will agglomerate into visibly sized clumps and will tumble in a gravity flow from the hopper outlet. The vibrating and tamping of this thixotropic material into the mold will merge the edges of the clumps together but will not substantially mix the bulk of differently colored clumps of materials together.
Further details of the invention and its advantages will be apparent from the detailed description and drawings included below.